During the operation of a digital Liquid Electro Printing (LEP) system, ink images are formed on the surface of a photo-imaging cylinder. These ink images are transferred to a heated offset roller and then to a print medium, such as a sheet of paper. The photo-imaging cylinder continues to rotate, passing through various stations to form the next image. A cleaning station cleans stray particles and cools the photo-imaging cylinder surface by placing an oil film on the surface with a wetting roller. Subsequently, a sponge roller lifts the oil film from the cylinder surface along with stray particulates and other contaminants.
The oil film produced by the wetting roller should be very uniform across the surface of the photo-imaging cylinder. Spatial or temporal variations in the film thickness can result in uneven cooling and cleaning of the photo-imaging cylinder surface. This, in turn, can produce variations in print quality. For example, higher temperature areas of the cylinder surface may react differently than cooler areas during photocharging, ink deposition, or the transfer of the ink image. Further, areas of the surface that receive less oil may retain stray ink particles from the previous image.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.